Tricity Bendix Strata CSIE 510 Temp problems?

My Grandparents have an Oven as listed above, it is a top oven/grill and main oven.
The book says that when the door is closed the oven should activate and the grill when the door is open. However they have often opened the oven to find the grill on and the food burnt. Please can someone tell me if the grill is supposed to be on when the door is closed and if not what the probem could possibly be.
The info for the cooker is as follows.

Model No. CSIE510W
Product No. 948523067
Serial No. 03900082

Kind Regards
Ed Hanson